U.S. patent number 7,939,970 [Application Number 12/843,198] was granted by the patent office on 2011-05-10 for variable frequency wind plant.
This patent grant is currently assigned to General Electric Company. Invention is credited to Robert William Delmerico, Einar Vaughn Larsen, Reigh Allen Walling.
United States Patent |
7,939,970 |
Walling , et al. |
May 10, 2011 |
Variable frequency wind plant
Abstract
A method and system for reducing the cost of a combined offshore
wind generation plant is provided by coupling the AC output of
plural wind turbine generators to a single AC-DC converter prior to
transmission of the DC power to an onshore DC-AC inverter site. The
wind speed is monitored at selected locations within the wind
plant, optionally, at selected turbine generators, and the
operating frequency of the AC-DC converter is adjusted in
accordance with a combine wind speed signal to permit operation of
the plural wind turbines as a group. AC-DC followed by DC-AC
conversions decouples the AC frequency produced by the wind
turbines and allows the turbines to operate at variable frequency
as a group.
Inventors: |
Walling; Reigh Allen (Clifton
Park, NY), Larsen; Einar Vaughn (Ballston Park, NY),
Delmerico; Robert William (Clifton Park, NY) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
43928281 |
Appl.
No.: |
12/843,198 |
Filed: |
July 26, 2010 |
Current U.S.
Class: |
307/84;
290/44 |
Current CPC
Class: |
F03D
7/0284 (20130101); H02J 3/381 (20130101); F03D
7/048 (20130101); H02J 3/40 (20130101); H02J
3/386 (20130101); H02P 9/04 (20130101); Y02E
10/76 (20130101); Y02E 10/72 (20130101); F05B
2270/32 (20130101); H02P 2101/15 (20150115); H02J
2300/28 (20200101) |
Current International
Class: |
H02J
1/00 (20060101); H02J 3/00 (20060101); H02P
9/04 (20060101); F03D 9/00 (20060101) |
Field of
Search: |
;307/84 ;290/44 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fureman; Jared J
Assistant Examiner: Parries; Dru M
Attorney, Agent or Firm: Dority & Manning, P.A.
Claims
What is claimed is:
1. A control method for a variable frequency wind plant, the wind
plant comprising a plurality of variable frequency wind turbine
generators, comprising: measuring wind speed at a plurality of
selected locations within the wind plant and generating respective
wind speed signals indicative of the measured wind; collecting and
applying the output from each of the plurality of wind turbine
generators to a common AC-DC converter; and, adjusting the
operating frequency of the common AC-DC converter based on the
plurality of measured wind speed signals, whereby the wind turbines
are operated at a variable frequency as a group.
2. The method of claim 1, wherein measuring wind speed and
generating wind speed signals comprises: providing a wind speed
signal from a plurality of anemometers associated individually with
selected of the plurality of wind turbine generators.
3. The method of claim 1, further comprising configuring selected
of the plurality of variable frequency wind turbine generators to
adjust their individual speed based on wind speed signals local to
the individual turbine.
4. The method of claim 1, wherein each of the plurality of variable
frequency wind turbine generators has a fixed relationship between
the turbine rotational speed and the frequency of the generated AC
output.
5. The method of claim 1, wherein selected of the plurality of
variable frequency wind turbine generators correspond to generators
configured to permit variation in the relationship between turbine
rotational speed and the frequency of the generated AC output.
6. The method of claim 1, further comprising: providing a central
control system; transmitting the plurality of wind speed signals to
the central control system; and, configuring the central control
system to produce a signal to adjust the operating frequency of the
common AC-DC converter.
7. The method of claim 6, wherein transmitting the plurality of
wind speed signals comprises conveying the wind speed signals to
the central control system by one of wire, fiber optic, and radio
communications.
8. A power system, comprising: a plurality of variable frequency
wind turbine generators; a plurality of wind speed measurement
devices that measure wind speed and generate a corresponding wind
speed signal; an AC-DC converter; a collection system configured to
collect generated power from each of said plurality of variable
frequency wind turbine generators and apply the collected generated
power to said AC-DC converter; and, a control system configured to
combine the wind speed signals from said plurality of wind speed
measurement devices into a combined wind speed signal and to
generate a control signal for said AC-DC converter to control the
operating frequency thereof based on the combined wind speed
signal.
9. The power system of claim 8, wherein each of the plurality of
variable frequency wind turbine generators has a fixed relationship
between the turbine rotational speed and the frequency of the
generated AC output.
10. The power system of claim 8, wherein selected of the plurality
of variable frequency wind turbine generators correspond to
generators configured to permit variation in the relationship
between turbine rotational speed and the frequency of the generated
AC output.
11. The power system of claim 8, wherein wind speed signals from
said plurality of wind speed measurement devices are conveyed to
the control system by one of wire, fiber optical, and radio
communication.
12. The power system of claim 11, wherein the plurality of wind
speed measurement devices correspond to a plurality of
anemometers.
13. The power system of claim 11, wherein selected of the plurality
of wind speed measurement devices are associated with selected of
the variable frequency wind turbine generators.
14. The power system of claim 8, further comprising: a DC-AC
inverter coupled to said AC-DC converter by a DC transmission line,
and, an AC power grid, wherein the output frequency of said DC-AC
inverter is configured to match the operating frequency of the AC
power grid.
15. A control method for a power system, the power system
comprising a converter configured to provide DC power from a
plurality of AC power sources operating at variable frequencies,
and an inverter configured to convert the DC power provided by the
converter to AC power at a single frequency, comprising: producing
signals based on a measured variable associated with the respective
operating frequency of selected ones of the plurality of AC power
sources; applying power generated by each of the plurality of AC
sources to the converter; controlling the operating frequency of
the converter in dependence on a control signal generated by
combining the signals produced; and wherein the plurality of AC
power sources correspond to a plurality of AC power generating wind
turbines and wherein producing signals corresponds to producing
signals based on measured wind speed in the vicinity of the
selected ones of the plurality of AC power generating wind
turbines.
16. The method of claim 15, wherein each of the plurality of AC
power generating wind turbines has a fixed relationship between the
turbine rotational speed and the frequency of the generated AC
power.
17. The method of claim 15, wherein selected of the plurality of
variable frequency wind turbine generators correspond to generators
configured to permit variation in the relationship between turbine
rotational speed and the frequency of the generated AC output.
18. The method of claim 15, wherein producing signals comprises
producing signals based on wind speed local to selected of the
plurality of AC power generating wind turbines.
Description
FIELD OF THE INVENTION
The present invention relates generally to the field of wind
generators, and, more particularly, to methods and systems to allow
for reducing the cost of operation of plural wind generating plants
and associated transmission systems.
BACKGROUND OF THE INVENTION
In distributed generation applications wherein the site for
generation is remote from the available electric grid or load
point, bulk power is often transmitted over long distances. In an
offshore wind farm, for example, power generated by individual wind
turbine generators is processed by power electronic converters to
convert variable voltage, variable frequency output to fixed
voltage, fixed frequency output. The outputs from the individual
generators are synchronized to the utility network frequency even
though the individual machines are running at different speeds and
hence outputting different frequencies.
The power generated from the turbines is then brought together by a
collection system that includes transformers and switchgear for
isolating individual turbines and stepping up the voltages, usually
to tens of kilovolts. The collection network is then cabled to an
off-shore substation that boosts up the voltage further, usually to
hundreds of kilovolts. It is then transmitted through subsea cable
to an on-shore substation, where it is tied to the utility network
through isolating switchgear and transformers.
For applications wherein bulk power is transmitted over long
distances, conventional alternating current (AC) transmission
provides technical challenges. Capacitance causes charging current
to flow along the length of the AC cable. Because the cable must
carry this current as well as the useful source current, this
physical limitation reduces the source carrying capability of the
cable. Because capacitance is distributed along the entire length
of the cable, longer lengths result in higher capacitance and
higher resulting charging current. As the cable system design
voltage is increased to minimize the line losses and voltage drop,
the charging current also increases.
DC transmission can be achieved more efficiently over longer
distances than AC transmission. Medium voltage (MV) or high voltage
(HV) DC transmission typically requires power electronic converters
which are capable of converting between HVAC and HVDC. In
conventional converter topologies, each switch of the converter is
designed to handle high voltages which may range from tens of
kilovolts to hundreds of kilovolts depending upon the application.
Such switches are typically arranged with series connection of
several semiconductor devices, such as insulated gate bipolar
transistors (IGBTs) and thyristors.
In view of these known complexities involved with generation,
collection and transmission of bulk power, there is a need for a
method and system to reduce the cost of the combined wind
generation plant and transmission system.
BRIEF DESCRIPTION OF THE INVENTION
Aspects and advantages of the invention will be set forth in part
in the following description, or may be obvious from the
description, or may be learned through practice of the
invention.
One exemplary embodiment of the present disclosure is directed to a
control method for a variable frequency wind plant, the wind plant
comprising a plurality of variable frequency wind turbine
generators. The method includes providing a wind speed signal from
selected locations within the wind plant. For example, wind speed
signals may be provided from individual wind speed measuring
devices, for example, anemometers, positioned at selected locations
within the wind plant or, optionally, associated with selected wind
turbines. The output from the plurality of wind turbine generators
is collected and applied to a common AC-DC converter. The operating
frequency of the common AC-DC converter is adjusted based on a
combined wind speed signal, so that the wind turbines may be
operated at a variable frequency as a group.
In particular embodiments, the wind speed signals may also be used
to adjust the individual speed of any one or group of the wind
turbines.
In some of the embodiments, the plurality of variable frequency
wind turbine generators have a fixed relationship between the
turbine rotational speed and the frequency of the generated AC
output, while in other embodiments variation in the relationship
between turbine rotational speed and the frequency of the generated
AC output is permitted.
In other embodiments, the method further provides transmitting the
wind speed signals to a central control system that is configured
to produce a signal to adjust the operating frequency of the common
AC-DC converter. In specific embodiments, the wind speed signal is
conveyed to the control system by one of wire, fiber optic, and
radio communications.
Another exemplary embodiment of the present disclosure is directed
to a power system that includes a plurality of variable frequency
wind turbine generators, a plurality of wind speed measurement
devices, an AC-DC converter, a collection system configured to
collect generated power from each of the plurality of variable
frequency wind turbine generators and apply the collected generated
power to the AC-DC converter, and a control system configured to
combine wind speed signals from the plurality of wind speed
measurement devices into a combined wind speed signal and to
generate a control signal for the AC-DC converter to control the
operating frequency thereof based on the combined wind speed
signal.
In certain embodiments, the power system also includes a DC-AC
inverter coupled to the AC-DC converter by a DC transmission line,
and an AC power grid, wherein the output frequency of the DC-AC
inverter is configured to match the operating frequency of the AC
power grid.
A further exemplary embodiment of the present disclosure is
directed to a control method for a power system, where the power
system comprises a converter configured to provide DC power from a
plurality of AC power sources operating at variable frequencies,
and an inverter configured to convert the DC power provided by the
converter to AC power at a single nominal frequency, comprising
producing signals based on a monitored variable associated with the
operating frequency of selected of the plurality of AC power
sources, applying power generated by each of the plurality of AC
sources to the converter, and controlling the operating frequency
of the converter in dependence on a combination of the signals
produced. In selected embodiments the monitored variable may
correspond to the rotational speed of a generator corresponding to
selected of the plurality of AC power sources.
In selected embodiments, the control method employs a plurality of
AC power sources corresponding to a plurality of AC power
generating wind turbines and produces signals corresponding to
signals based on wind velocity in the vicinity of selected of the
plurality of AC power generating wind turbines.
Variations and modifications can be made to these exemplary
embodiments of the present disclosure.
These and other features, aspects and advantages of the present
invention will become better understood with reference to the
following description and appended claims. The accompanying
drawings, which are incorporated in and constitute a part of this
specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
A full and enabling disclosure of the present invention, including
the best mode thereof, directed to one of ordinary skill in the
art, is set forth in the specification, which makes reference to
the appended figures, in which:
FIG. 1 is a schematic block diagram of a generation, collection,
and bulk power transmission system in accordance with present
technology.
Repeat use of reference characters throughout the present
specification and appended drawings is intended to represent same
or analogous features or elements of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Reference now will be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
drawings. Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment, can be used
with another embodiment to yield a still further embodiment. Thus,
it is intended that the present invention encompass such
modifications and variations as come within the scope of the
appended claims and their equivalents.
Generally, the present disclosure is directed to methods and
apparatus for reducing the cost of a combined wind generation plant
corresponding to a plurality of wind turbines or generators and an
associated transmission system. The present technology provides for
significant cost savings by employing a single AC-DC converter to
connect a plurality of wind turbine generators to a DC transmission
line. By such technique, DC power may be transmitted to a remote
conversion location where the DC power is converted to AC for
delivery to an AC grid.
An aspect of the present subject matter is that the conversion of
AC to DC and from DC back to AC decouples the AC frequency produced
by the wind turbines from the AC frequency of the remote AC grid.
This allows the wind turbines to operate at a variable frequency,
as a group, to achieve many of the efficiency advantages of
variable speed operation of the wind turbines without the burden of
providing power conversion functionality at each wind turbine in
order to permit variable speed operation in a fixed-frequency
collection system.
The individual wind turbines could use synchronous generators,
permanent magnet generators, or generators with limited speed
variation such as induction generators. The frequency of the
offshore collection system is chosen such that the rotational speed
of the wind turbines are optimized as a group. Where the generator
of each wind turbine allows limited variation in speed, this speed
variation can be applied for mechanical oscillatory damping, loads
management, or further optimizing of the speed of the individual
wind turbine generator.
It should be appreciated that while the present subject matter is
described as relating to offshore collection systems, such
technology is equally applicable to land based installations so
that the offshore aspect of the described subject matter is not to
be considered a specific limitation of the present subject
matter.
With reference now to FIG. 1, it will be seen that there is
illustrated a schematic block diagram of a generation, collection,
and bulk power transmission system in accordance with present
technology. The various components of the system include a
plurality of wind turbines 10, 12, 14, 16, each having a generator
that has a fixed relationship between the turbine rotational speed
and the frequency of the generated AC output. Alternatively, the
generator may correspond to one that allows a small degree of
variation in this relationship between rotational speed and AC
frequency, but which does not pass all of the power output
generated by the wind turbine through a power electronic conversion
process at each individual wind turbine generator.
The present subject matter also provides a collection system
consisting of cables or lines 20 that connect the output of the
individual wind turbine generators10, 12, 14, 16 to a central power
rectifier 30. Those of ordinary skill in the art will appreciate
that while a single line is illustrated in the FIGURE to represent
the collection system, such is intended to represent a plural phase
AC collection system.
The collection system cables or lines 20 convey the generated power
to central power rectifier 30 where the variable-frequency power
produced by wind turbines 10, 12, 14,16 is converted to direct
current at a suitable voltage for transmitting the power to remote
inverter 40 or a multiplicity of such inverters. Inverter 40 is
provided to convert the power from DC to AC at a frequency and
voltage compatible with the AC grid to which they are connected. A
DC line or cable 50 is provided to transmit the power from the
rectifier 30 to inverter(s) 40.
In accordance with the present subject matter, a device to sense
wind velocity is provided at the location of each wind turbine 10,
12, 14, 16. In an exemplary configuration, the wind speed sensing
device may correspond to anemometers 60, 62, 64, 66. Alternatively,
wind speed sensing devices may be separately placed at selected
locations within the wind plant. Such separate placement may or may
not be in association with any particular wind turbine and may or
may not correspond in number to the number of wind turbines within
the wind plant.
Central control system 70 is configured to determine the desired
operating frequency of the AC collection system such that the power
output, mechanical loads, or efficiency of the wind turbines 10,
12, 14,16 are collectively optimized. A communication device 80 is
provided to transmit wind velocity measurements from anemometers
60, 62, 64, 66 to central control system 70. In exemplary
configurations, communications device 80 may include, but is not
limited to, wire, fiber optic, and wireless transmission such as
radio communications. It is noted that the terms wind velocity and
wind speed as variously used herein are viewed for present purposes
as synonymous terms.
Central control 70 includes a system for controlling rectifier 30
by way of control link 90 that establishes the operating frequency
of the AC collection system. Anemometers 60, 62, 64, 66 measure the
wind velocity at each of the wind turbines 10, 12, 14, 16, or,
optionally, at selected locations within the wind plant and
transmit the wind speed data to the central control system 70 via
the communications link or system 80. Central control system 70
determines the AC frequency at which the local system composed of
the wind turbines 10, 12, 14, 16 and collection system 20 should be
operated such that the speed of the wind turbines optimizes power
production, mechanical load mitigation, or efficiency of the wind
turbines 10, 12, 14, 16 as a collective group. The individual wind
turbines 10, 12, 14, 16 may have the ability to adjust their
individual speed over a limited range to further optimize power
production, load management, or efficiency due to wind conditions
local to the individual turbine.
Power rectifier 30 converts the variable frequency AC power
generated by wind turbines 10, 12, 14, 16 to direct current at a
high voltage of magnitude suitable for transmission of the power to
a remote location over DC line or cable 50. At the remote
termination or terminations of line or cable 50, the power is
converted to AC by inverter 40 at an appropriate voltage and
frequency for delivery to loads via an AC transmission system.
As previously noted, the present technology may be most
advantageously employed in an offshore wind plant application due
to the fact that DC transmission of the power from the offshore
wind plant is often favored or necessary due to the requirement to
use a long insulated cable to bring the power ashore. Where DC
transmission is used with a conventional fixed-frequency collection
system design, some form of conversion is needed at each wind
turbine in order to facilitate variable speed operation, and the
power is converted again to connect the offshore collection system
to a DC cable. Another reason that the present technology could
have particular application offshore is that offshore wind speed is
generally more uniform than in an onshore wind plant, due, at least
in part, to the lack of orographic features. Under such offshore
operating conditions, it may be advantageous to employ only a
relatively small number of wind speed sensors to achieve desired
operational characteristics as described herein.
This written description uses examples to disclose the invention,
including the best mode, and also to enable any person skilled in
the art to practice the invention, including making and using any
devices or systems and performing any incorporated methods. The
patentable scope of the invention is defined by the claims, and may
include other examples that occur to those skilled in the art. Such
other examples are intended to be within the scope of the claims if
they include structural elements that do not differ from the
literal language of the claims, or if they include equivalent
structural elements with insubstantial differences from the literal
languages of the claims.
* * * * *